The present invention relates to enhancement of stability of a prostanoic compound acids having at least one oxo group on the .omega. chain.
Generally, quality of a pharmaceutical product is controlled based on the policy that contamination should be prevented and that the quality of the product should be consistent. Accordingly, the product should have at least a certain degree of purity which can be maintained for a certain period. This is important especially in the case of a compound exhibiting a physiological activity in a small amount, such as a prostanoic acid compound.
The Prostanoic acid compound, which have general structural characteristics of naturally-occurring prostaglandins (PGs), are represented by the following formula. ##STR1##
According to structure of the 5-membered ring, natural PGs can be classified into PGAs, PGBs, PGCs, PGDs, PGEs, PGFs, PGGs, PGHs, PGIs and PGJs. They are further grouped, based on the unsaturations at 5, 6 positions and at 13, 14 positions, into PG.sub.1 s (13,14-unsaturated), PG.sub.2 s (5,6 and 13,14-diunsaturated) and PG.sub.3 s (5,6-, 13,14- and 17,18-triunsaturated).
PGFs are further classified according to the configuration of hydroxyl group at 9 position into .alpha. form (hydroxyl group present in alfa configuration) and .beta. form (hydroxyl group present in beta configuration).
Although these natural PGs have various pharmacological activities, they are commonly unstable, and are liable to be decomposed by acids, bases or heat. Moisture is also a factor affecting the stability of PGs, and PGs should be stored in an anhydrous condition or in a condition in which the moisture content is as low as possible.